The communication method being developed as an LTE (Long Term Evolution) by 3GPP (3rd Generation Partnership Project) aims at a high throughput of at least 100 Mbps. Additionally, future traffic is expected to increase along with today's remarkable development of diversification in various communication services. In order to cope with such future traffic, communication methods having a high throughput have also been demanded. For this purpose, many inventions have been made in order to improve a throughput of the entire communication system.
The wireless communication technology has continuously been evolved with the aforementioned inventions and the like. This evolution can be a considered as an outcome of the research and development in various fields, including selection of a frequency band of radio waves, transmission methods, encoding/decoding, error control, multiplexing, multiple accesses, efficient use of frequency bands, and the like. Furthermore, the evolution can also be considered as an outcome of the research and development of communication systems as a whole.
In order to efficiently use frequency bands in the above fields, it is necessary to improve the efficiency of mapping subcarriers. Subcarrier mapping is carried out in an HSDPA (High Speed Down-link Packet Access) of the “Release 5” standard or the like. In the HSDPA, a modulation method or an encoding method suitable for high-speed communication is assigned to a channel of good quality, while a modulation method or an encoding method having high stability is assigned to a channel of poor quality. Thus, the communication loss in the entire communication system is reduced by identifying the channel quality and accordingly changing modulation methods and/or encoding methods.
Specifically, if a modulation method for high-speed communication is used in a case where the channel quality is low (the communication environment is bad), many communication errors will occur. Error correction or an error correction process such as request repeat needs to be performed each time an error occurs. Therefore, use of a modulation method in consideration of the communication quality or the like contributes to reduction of the communication loss in the entire communication system.
That is, high-speed communication is not necessarily established in the case where a modulation method capable of high-speed communication or the like is used. It is important to examine the benefit of the entire communication system in consideration of many factors including the channel quality.
For example, if a control signal for communication is lost, the intended purpose of signals (data) correctly received becomes unknown. Thus, the received signals (data) should be discarded eventually. In another example, if part of information for error correction is lost, the receiving process is recognized as failure even though correct signals have been received.
Therefore, when communication of a control signal having high importance (systematic bit) or the like is performed under a more secure environment, a throughput can be improved as a whole.
Meanwhile, in the HSDPA, it is important to conduct mapping of subcarriers (frequency resources) with use of a CQI (Channel Quality Indicator) so as to efficiently control resource mapping for a mobile station.
For example, those techniques are disclosed in Patent Documents 1 and 2.
Patent Document 1 discloses a technique of improving communication efficiency by selecting a transmission schedule depending upon the type of information to be transmitted. Furthermore, Patent Document 1 discloses a technique of selecting a modulation method and an encoding ratio for each subcarrier with use of a table of MCS selection information in which CQIs are associated with encoding ratios.
Patent Document 2 discloses a technique of selecting a subcarrier with use of a CQI and further selecting a modulation method and an encoding method for the selected subcarrier with use of a frequency hopping pattern and the CQI.
Patent Document 1: WO2005/020488
Patent Document 2: Japanese laid-open patent publication No. 2006-325264